Monday 18 December 2000
The reasons why some women with a common sexually transmitted infection have a greater risk of developing cervical cancer than other women with an identical infection have been revealed in the biggest study of its kind published in December's British Journal of Cancer.
Researchers from The Institute of Cancer Research, funded by The Cancer Research UK, say that the answer lies in women's sexual and smoking habits.
Experts already know that tens of thousands of women in the UK are infected every year with the sexually transmitted human papillomavirus (HPV) which causes no visible symptoms and which most women don't know they have.
They also know that this infection is linked to cervical cancer because studies of women with the disease show that virtually all patients are infected with HPV.
Until now, experts were unsure about which of a number of factors, together with HPV infection, were important in predicting whether women went on to develop the disease. These factors included women's number of sexual partners, at what age they started having sex, and whether they smoked or were on the contraceptive pill.
What researchers have now discovered is that women with HPV who smoke are more likely to develop CIN3, which is a precursor of cervical cancer, than women with HPV who don't smoke. But women who take the pill are at little or no increased risk.
Researcher Dr Judith Deacon from The Institute says: "For a long time scientists have suspected that smoking increases the risk of women developing cervical cancer. But because smoking is strongly related to sexual behaviour it has been very difficult to disentangle the roles of the different risk factors. This study now confirms the role of smoking."
The study also shows that women with HPV who first had sex in their early teens are at greatest risk.
Dr Deacon says: "This tells us that HPV infection carries a greater risk of causing disease the longer women have it.
"At a practical level the main message of our study is that women who want to reduce their risk of cervical cancer should stop smoking. They should of course also have a regular smear test, which has been shown to prevent the great majority of cervical cancers."
Prof. Julian Peto, Cancer Research UK Chair of Epidemiology at The Institute of Cancer Research says: "Our results also have implications for future developments in screening and vaccine research. Latent HPV may often be undetectable by any screening test and is unlikely to be eliminated by vaccination. HPV vaccination before sexual activity begins may thus be necessary to achieve the long-term aim of preventing cervical cancer by eliminating the infection that causes it."
The project is part of a larger study of 61,000 women who attended the cervical screening programme in the Greater Manchester area between 1988 and 1993.
Researchers interviewed 200 women who had HPV and had gone on to develop CIN3, 200 who only had HPV infection and 200 with neither HPV nor pre-cancerous cervical cells. The lifestyles as well as the gynaecological, reproductive and sexual histories of these three groups of women were compared. Dr Peter Rigby, Chief Executive of The Institute of Cancer Research commented: 'This important research makes the causes of cervical cancer much clearer. With this new knowledge we can work to prevent the disease by explaining to women the lifestyle factors that put them at risk.'
The Director General of The Cancer Research UK Prof. Gordon McVie says: "This study is important because it is the biggest study of its kind to distinguish between risk factors for HPV and cervical cancer. In the past it was always assumed that the risk factors for cervical cancer would be identical to those for HPV infection. But the evidence now clearly points towards persistent HPV infection and smoking being the major culprits for cervical cancer."
British Journal of Cancer Vol 83 (11)
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Notes to editors
- The Institute of Cancer Research was established in 1909 to carry out research into the causes of cancer and to develop new strategies for its prevention, diagnosis, treatment and cure. It works in a unique partnership with the Royal Marsden NHS Trust, forming the largest comprehensive cancer centre in Europe. This relationship enables us to stay in close daily contact with those on the frontline in the fight against cancer - the clinicians, the carers and most importantly, the patients.
- Cancer Research UK is Britain's foremost cancer charity and the European leader in anti-cancer drug development. It is dedicated to finding new ways of curing, treating and preventing cancer.
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